Lubrication pump for inter-axle differential

ABSTRACT

An inter-axle differential assembly comprises an input shaft, an output shaft arranged coaxially with respect to each other, differential gearing and a dedicated reversible lubrication pump disposed between the input and output shafts. The reversible gerotor type lubrication pump includes a rotor driven by the input shaft, and an impeller, both disposed within a pump body coupled to a side gear drivingly connected to the output shaft. Thus, the lubrication pump generates lubricant flow only during the differential action between the input shaft and the output shaft, i.e. only when needed and at a flow rate proportional to the speed difference across the differential assembly. An oil flow generated by the lubrication pump is supplied to various components of the inter-axle differential assembly through a gallery of fluid passages.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 09/761,724,filed on Jan. 18, 2001 now U.S. Pat. No. 6,855,083.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates broadly to inter-axle differentialassemblies and, more particularly, to a dedicated lubrication pump foran inter-axle differential assembly.

2. Description of the Prior Art

Motor vehicles with solidly connected multiple drive axles are commonlyequipped with an inter-axle differential assembly, commonly arranged ina vehicular transmission transfer case or tandem axle power divider toallow torque balance between the drive axles during the vehiclecornering, to compensate for tire size differences, etc., i.e. whenthere is any physical requirement for speed difference between the driveaxles. The inter-axle differential assemblies are widely employed fortandem drive axles of heavy-duty trucks for on-and off-road service as apower divider.

These motor vehicles are, on occasion, driven in situations where theremay be unequal traction conditions between the tires of the differentdrive axles. If the traction condition at any tire falls below thatrequired for sufficient traction effort, high-speed inter-axledifferential conditions may occur. These high-speed differentialconditions may be potentially severely damaging to critical differentialassembly components, such as shaft bearing surfaces as well as rollingcontact surfaces of the differential assembly, due to lack oflubrication.

In such drive axles it is common to have a supply of lubricant in atransfer case or axle housing and to provide positive lubricant pressureto the input and output shaft journals and the inter-axle differentialthat are disposed above the level of lubricant in the housing to preventdamaging the differential gear components during these high speeddifferential conditions. However, current lubrication pumps fordifferential assemblies are driven continuously while the vehicle is inmotion, although lubrication supply is only needed during occasionalconditions of relatively high-speed levels of differential action as itis well known to those skilled in the art. The continuously drivenlubrication pump operates and consumes engine power irrespective of theamount of lubrication needed by the shaft journals and other componentsof the inter-axle differential, thus causing unnecessary parasiticlosses in a vehicle power transmission and increasing fuel consumption.

Thus it has been desired to provide a low-cost and convenient way toincorporate a lubricant pump for providing positive flow of lubricant tothe shaft journals and the inter-axle differential assembly only asrequired.

SUMMARY OF THE INVENTION

The present invention alleviates the drawbacks of the prior art. Thepresent invention provides an inter-axle differential assembly having adedicated lubrication pump. The lubrication pump is drivingly coupled totwo differentially rotating members of the differential assembly, and,thus, supplies lubricant only when differential action occurs. Thehydraulic pump provides volumetric flow of lubricant that varies indirect proportion to the relative (or differential) rotational speed ofthe rotating members.

In accordance with the preferred embodiment of the present invention,the inter-axle differential assembly comprises an input shaft, an outputshaft arranged coaxially with respect to each other, a differentialgearing and the dedicated lubrication pump disposed between the inputand output shafts. The lubrication pump is provided solely for thepurpose of lubricating the shaft journals and the inter-axledifferential gearing, and only when needed, i.e. the pump generateslubricant flow only during the differential action between the inputshaft and the output shaft, and at a flow rate in proportion to thespeed differential.

In accordance with the preferred embodiment of the present invention,the pump is of the gerotor type, and the differential is of the bevelgear type. However, other types of pumps, such as gear or vane typepumps, are within the scope of the present invention, as well as othertypes of differentials, such as the spur gear type. The lubrication pumpincludes a rotor driven by the input shaft, and a housing coupled to aside gear drivingly connected to the output shaft. An oil flow generatedby the lubrication pump is supplied to the shaft journals and theinter-axle differential gearing through a gallery communicating withpassages in the input and output shafts which supply lubricant to thejournals for these shafts and to the inter-axle differential assembly.

Alternatively, the pump housing is coupled directly to the output shaft.

Therefore, the inter-axle differential assembly in accordance with thepresent invention includes the dedicated lubrication pump, compactlydisposed between the input and output shafts, that lubricates thedifferential assembly components only when needed, thus providing betterefficiency and lower fuel consumption.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become apparent froma study of the following specification when viewed in light of theaccompanying drawings, wherein:

FIG. 1 is a longitudinal cross-sectional view of a tandem axle powerdivider that houses an inter-axle differential of the present invention;

FIG. 2 is a longitudinal cross-sectional view of the inter-axledifferential in accordance with the first embodiment of the presentinvention;

FIG. 3 is a longitudinal cross-sectional view of a portion of theinter-axle differential in accordance with the first embodiment of thepresent invention showing a preferred embodiment of a gerotorlubrication pump;

FIG. 4 is a longitudinal cross-sectional view of a portion of theinter-axle differential in accordance with the first embodiment of thepresent invention showing alternative embodiment of the gerotorlubrication pump;

FIG. 5 is a longitudinal cross-sectional view of a portion of theinter-axle differential in accordance with the second embodiment of thepresent invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The preferred embodiments of the present invention will now be describedwith the reference to accompanying drawings.

Referring to FIG. 1, an inter-axle differential assembly 10 of thepresent invention disposed in a housing 4 of a tandem axle power dividerindicated generally at 2, is illustrated. The housing 4 is ordinarilyprovided with a supply of lubricant, such as lubrication oil, therein.

The inter-axle differential assembly 10 in accordance with the firstembodiment of the present invention, illustrated in detail in FIG. 2,comprises an input shaft 14 rotatably supported in a bearing assemblyindicated generally at 16, a differential spider 32 drivingly coupled tothe input shaft 14 and provided with a plurality of pinion gears 34rotatably mounted thereon, a first side gear 20 and a second side gear44 meshing with the pinion gears 34, an output shaft 30 drivinglyconnected to the first side gear 20, and a dedicated lubrication pump 50disposed between the input shaft 14 and the output shaft 30 and solelyfor the purpose of lubricating components of the inter-axle differentialassembly 10 during the differential action between the input shaft 14and the output shaft 30.

The input shaft 14 rotatably supported in a bearing assembly indicatedgenerally at 16, and has a yoke 18 attached thereto, which is adaptedfor receiving torque from a vehicle driveline (not shown). Thedifferential spider 32 drivingly engages the input shaft 14 by anyappropriate means, preferably through a spline connection 36. Thus,input torque is transmitted directly to the differential spider 32. Inmost applications, the number of the pinion gears 34 will be four, butthe number can be as low as two and can be higher than four, althoughmost practical applications would probably not contain more than sixpinion gears.

The first side gear 20 is journalled in a second bearing assemblyindicated generally at 22, and has a reduced diameter pilot portion 24of the input shaft 14 journalled therein. The first side gear 20includes a flange portion 26 integrally formed with a sleeve portion 28.The flange portion 26 is provided with a plurality of side gear teeth 27formed thereon for meshing with the pinion gears 34. The sleeve portion28 of the first side gear 20 is drivingly coupled with the output shaft30. An outboard end of the output shaft 30 is adapted for connection tothe rear drive axle (not shown) of the motor vehicle.

The second side gear 44 is rotatably mounted to the input shaft 14 by asleeve bearing or bushing 48 for free rotation thereon. It will beappreciated that any other appropriate type of bearings, such as needlebearings, are also applicable. The second side gear 44 has a pluralityof gear teeth 46 thereon engaging the pinion gears 34.

A lubrication pump 50, in accordance with the first embodiment of thepresent invention, is disposed between the input shaft 14 and the outputshaft 30 of the inter-axle differential 10 within the sleeve portion 28of the first side gear 20. In the preferred embodiment, the lubricationpump 50 is a gerotor pump.

The reversible unidirectional flow gerotor pump 50, well known in theprior art and illustrated in detail in FIG. 3, comprises a rotor 52having a plurality of external teeth, an impeller 54 having a pluralityof internal teeth which are in meshing engagement with external teeth ofthe rotor 52, and a pump body 56 housing the rotor 52 and the impeller54. The rotor 52 is eccentrically arranged relative to the impeller 54and is drivingly connected to the input shaft 14 through a rotor shaft58 having a substantially smaller diameter then the pilot portion 24 ofthe input shaft 14, as seen in FIG. 2. In general, the rotor 52 has oneless tooth than the impeller 54, such that driving of the rotor 52 willin turn cause driving of the impeller 54. The pump body 56 is secured tothe side gear 20 within its sleeve portion 28 by means of a pin 64received in an arcuate groove 65 formed in the pump body 56. An inletport 60 and an outlet port 62 are formed in the pump body 56. Relativerotation of the rotor 52 to the impeller 54 thus provides a series ofvariable volume chambers within pump 50, resulting in the build up offluid pressure and pumping of lubricant in response to relative rotationof the rotor 52 and impeller 54, and thus in response to differentialrotation between the input shaft 14 and the first side gear 20.Obviously, volumetric flow of lubricant produced by the lubrication pumpvaries in direct proportion to the differential rotational speed of theinput and output shafts.

The pump body 56 is housed within the sleeve portion 28 of the firstside gear 20 and located angularly by the pin 64 in the arcuate groove65 formed in an outer peripheral surface of the pump body 56. The groove65 extends angularly around 90° of the outer peripheral surface of thepump body 56. Consequently, the pump body 56 is allowed to rotate 90°relative to the first side gear 20 depending on a relative direction ofrotation of the rotor 52 with respect to the first side gear 20. In thisway, the pump body 56 exchanges positions of the inlet port 60 and theoutlet port 62 relative to the first side gear 20 in order to provide areversible pumping function. Thus, the switching of ports 60 and 62allows the pump 50 to provide a unidirectional flow of lubricantregardless of the direction of the rotation of the rotor 52.

Referring again to FIGS. 2 and 3, the lubricant under pressure flowsfrom the outlet port of the lubrication pump 50 (the second port 62 inFIG. 3) through a gallery of fluid passages including a passage 70provided in the input shaft 14 to lubricate the components of theinter-axle differential 10 via a number of cross passages, such as across passage 72 for lubricating the sleeve bearing 48. Additionally,the inter-axle differential assembly 10 may have supplemental lubricantdelivery means, such as a splash diversion and delivery channels (notshown).

The inlet port 60 of the pump 50 is in fluid communication with an inletpassage 76 provided in a differential support carrier 75, trough aninlet cross passage 78 in the sleeve portion 28 of the first side gear20 between seal rings 80. Alternatively, as shown in a lower portion ofFIG. 3, pair of annular lip seals 80′ may be used to seal the inletpassage 76. The inlet passage 76 is in turn fluidly connected to thesupply of lubricant disposed in the housing 4 of the tandem axle powerdivider 2, and may be fitted with a check valve (not shown) or anelevated oil reservoir (not shown) to aid in pump priming.

It will be appreciated that any other appropriate types of reversibleunidirectional flow hydraulic pumps such as gear, vane or wobble pintype, well known in the prior art, are within the scope of the presentinvention.

FIG. 4 illustrates an alternative embodiment of the reversible gerotorlubrication pump used in the inter-axle differential assembly 10 inaccordance with the first embodiment of the present invention. Aninboard end 15 of the input shaft 14 is rotatably supported in thesleeve portion 28 of the first side gear 20. A dedicated lubricationpump 150, preferably a conventional gerotor pump of reversibleunidirectional flow type, is disposed within the sleeve portion 28 ofthe first side gear 20 adjacent to the inboard end 15 of the input shaft14. The lubrication gerotor pump 150 comprises a rotor 152, an impeller154, and a port plate 157 having a first port 160 and a second port 162.The rotor 152 is drivingly connected to the input shaft 14 through arotor shaft 158. An outlet passage 163 is formed within the tubularrotor shaft 158.

The lubricant under pressure flows from the outlet port 162 of thelubrication pump 150 through the passage 170 drilled in the input shaft14 to lubricate the components of the inter-axle differential 10 via anumber of cross passages, such as cross passages 72.

The port plate 157 is located angularly by a pin 164 in an arcuategroove 165 formed on an outer peripheral surface of the port plate 157.The groove 165 is angularly extended around an outer peripheral surfaceof the port plate 157 to approximately 180°. Consequently, the portplate 157 is allowed to rotate 180° relative to the first side gear 20depending on a relative direction of rotation of the pump rotor 152 withrespect to the first side gear 20. In this way, the port plate 157exchanges positions of the inlet port 160 and the outlet port 162relative to the first side gear 20 in order to provide a reversiblepumping function. Thus, the switching of the ports 160 and 162 allowsthe pump 150 to provide a unidirectional flow of lubricant regardless ofthe direction of the rotation of the rotor 152.

The inlet port 160 of the pump 150 is in fluid communication with theinlet passage 76 provided in the differential support carrier 75, troughan inlet cross passage 78 in the sleeve portion 28 of the first sidegear 20 between seal rings 80. Alternatively, as shown in a lowerportion of the FIG. 4, pair of annular lip seals 80′ may be used to sealthe inlet passage 76. It will be appreciated that any other appropriatesealing device for sealing the inlet passage 76 is within the scope ofthe present invention. The inlet passage 76 is fluidly connected to thesupply of lubricant disposed in the housing 4 of the tandem axle powerdivider 2, and may be fitted with a check valve (not shown) or anelevated oil reservoir (not shown) to aid in pump priming.

In accordance with the second embodiment of the present invention,illustrated in FIG. 5, an inboard end 215 of an input shaft 214 isrotatably supported in a tubular inboard end 231 of an output shaft 230.A dedicated lubrication pump 250, preferably of conventional reversibleunidirectional gerotor type, is disposed within the tubular inboard end231 of the output shaft 230 adjacent to the inboard end 215 of the inputshaft 214. The lubrication gerotor pump 250 comprises a rotor 252, animpeller 254, and a port plate 257 having an inlet port 260. The rotor252 is drivingly connected to the input shaft 214 through a rotor shaft258. An outlet port 262 is provided as a passage within the tubularrotor shaft 258.

The lubricant under pressure flows from the outlet port 262 of thelubrication pump 250 through a passage 270 drilled in the input shaft214 to lubricate the components of the inter-axle differential 10 via anumber of cross passages, such as cross passages 272. The inlet port 260of the pump 250 is in fluid communication with an inlet passage 276provided in a differential support carrier 275, trough an inlet crosspassage 178 in the tubular inboard end 231 of the output shaft 230between seal rings 280. Alternatively, as shown in a lower portion ofthe FIG. 5, pair of annular lip seals 280′ may be used to seal the inletpassage 276. It will be appreciated that any other appropriate sealingdevice for sealing the inlet passage 276 is within the scope of thepresent invention. The inlet passage 276 is fluidly connected to thesupply of lubricant disposed in the housing 4 of the tandem axle powerdivider 2, and may be fitted with a check valve (not shown) or anelevated oil reservoir (not shown) to aid in pump priming.

Therefore, a novel arrangement of the inter-axle differential assemblyin accordance with the present invention including the dedicatedlubrication pump provides a compact, efficient and low-cost solution forlubricating components of the inter-axle differential assembly only whenneeded. The present arrangement of the inter-axle differential assemblysubstantially reduces parasitic losses associated with poweringlubrication pumps.

The foregoing description of the preferred embodiments of the presentinvention has been presented for the purpose of illustration inaccordance with the provisions of the Patent Statutes. It is notintended to be exhaustive or to limit the invention to the precise formsdisclosed. Obvious modifications or variations are possible in light ofthe above teachings. The embodiments disclosed hereinabove were chosenin order to best illustrate the principles of the present invention andits practical application to thereby enable those of ordinary skill inthe art to best utilize the invention in various embodiments and withvarious modifications as are suited to the particular use contemplated,as long as the principles described herein are followed. Thus, changescan be made in the above-described invention without departing from theintent and scope thereof. It is also intended that the scope of thepresent invention be defined by the claims appended thereto.

1. An inter-axle differential assembly for a vehicular powertransmission unit provided with a supply of lubricant, said inter-axledifferential assembly comprising: a differential input shaft; adifferential output shaft; a differential gearing, said a differentialgearing including: a first side gear and a second side gear arrangedcoaxially relative to said input shaft and rotatable relative to saiddifferential input shaft, said first side gear is drivingly coupled tosaid output shaft; a differential spider drivingly connected to saidinput shaft; and a plurality of pinion gears rotatably mounted to saiddifferential spider and drivingly engaging said first side gear and saidsecond side gear to allow differential rotation thereof; a dedicatedlubrication pump for lubricating components of said differentialassembly, said pump mounted between said input shaft and said outputshaft, wherein said pump generates lubrication flow wheneverdifferential action between said differential input shaft and saiddifferential output shaft occurs, said lubrication pump including arotor non-rotatably coupled to said input shaft and an impellerpositioned within said first side gear, wherein said rotor is rotatablydisposed within said impeller and is operative upon rotation withrespect to said impeller; said lubrication pump being axially spacedfrom both said differential input shaft and said differential outputshaft; a hydraulic fluid suction passage providing an inlet fluidcommunication passage between said supply of lubricant and an inlet portof said lubrication pump; and a gallery of fluid passages supplying saidlubricant for lubricating said components of said inter-axledifferential assembly; said gallery of fluid passages fluidly connectedto an outlet port of said lubrication pump.
 2. The inter-axledifferential assembly as defined in claim 1, wherein said lubricationpump is a reversible unidirectional pump.
 3. The inter-axle differentialassembly as defined in claim 1, wherein said first side gear includes asleeve portion receiving at one end thereof said input shaft rotatablymounted therein and said output shaft at the other end for drivinglycoupling thereto, said sleeve portion of said first side gear housessaid lubrication pump therewithin.
 4. The inter-axle differentialassembly as defined in claim 3, wherein said inlet fluid communicationpassage includes an inlet passage formed in said sleeve portion of saidfirst side gear.
 5. The inter-axle differential assembly as defined inclaim 1, wherein said lubrication pump comprises a gerotor pump.
 6. Aninter-axle differential assembly for a vehicular power transmission unitprovided with a supply of lubricant, said inter-axle differentialassembly comprising: a differential input shaft; a differential outputshaft; a differential gearing, said a differential gearing including: afirst side gear and a second side gear arranged coaxially relative tosaid input shaft and rotatable relative to said differential inputshaft, said first side gear is drivingly coupled to said output shaft; adifferential spider drivingly connected to said input shaft; and aplurality of pinion gears rotatably mounted to said differential spiderand drivingly engaging said first side gear and said second side gear toallow differential rotation thereof; a dedicated lubrication pump forlubricating components of said differential assembly, said pump mountedbetween said input shaft and said output shaft, wherein said pumpgenerates lubrication flow whenever differential action between saiddifferential input shaft and said differential output shaft occurs, saidlubrication pump including a rotor non-rotatably coupled to said inputshaft and an impeller positioned within said first side gear, whereinsaid rotor is rotatably disposed within said impeller and is operativeupon rotation with respect to said impeller; a hydraulic fluid suctionpassage providing an inlet fluid communication passage between saidsupply of lubricant and an inlet port of said lubrication pump; and agallery of fluid passages supplying said lubricant for lubricating saidcomponents of said inter-axle differential assembly; said gallery offluid passages fluidly connected to an outlet port of said lubricationpump; said lubrication pump comprising a vane pump.
 7. An inter-axledifferential assembly for a vehicular power transmission unit providedwith a supply of lubricant, said inter-axle differential assemblycomprising: a differential input shaft; a differential output shaft; adifferential gearing, said a differential gearing including: a firstside gear and a second side gear arranged coaxially relative to saidinput shaft and rotatable relative to said differential input shaft,said first side gear is drivingly coupled to said output shaft; adifferential spider drivingly connected to said input shaft; and aplurality of pinion gears rotatably mounted to said differential spiderand drivingly engaging said first side gear and said second side gear toallow differential rotation thereof; a dedicated lubrication pump forlubricating components of said differential assembly, said pump mountedbetween said input shaft and said output shaft, wherein said pumpgenerates lubrication flow whenever differential action between saiddifferential input shaft and said differential output shaft occurs, saidlubrication pump including a rotor non-rotatably coupled to said inputshaft and an impeller positioned within said first side gear, whereinsaid rotor is rotatably disposed within said impeller and is operativeupon rotation with respect to said impeller; said rotor of saidlubrication pump being non-rotatably coupled to said differential inputshaft through a rotor shaft extending between said input shaft and saidrotor; a hydraulic fluid suction passage providing an inlet fluidcommunication passage between said supply of lubricant and an inlet portof said lubrication pump; and a gallery of fluid passages supplying saidlubricant for lubricating said components of said inter-axledifferential assembly; said gallery of fluid passages fluidly connectedto an outlet port of said lubrication pump.